//Different validations:
 NSString * inputStr = @"Hey ";

//Check length
[inputStr length]

//Coming from server, check if its NSNull
[inputStr isEqual:[NSNull null]] ? nil : inputStr

//For validation in allowed character set
-(BOOL)validateString:(NSString*)inputStr
{
    BOOL isValid = NO;
    if(!([inputStr length]>0))
    {
        return isValid;

    }

    NSMutableCharacterSet *allowedSet = [NSMutableCharacterSet characterSetWithCharactersInString:@".-"];
    [allowedSet formUnionWithCharacterSet:[NSCharacterSet decimalDigitCharacterSet]];
    if ([inputStr rangeOfCharacterFromSet:[allowedSet invertedSet]].location == NSNotFound)
    {
        // contains only decimal set and '-' and '.'

    }
    else
    {
        // invalid
        isValid = NO;

    }
    return isValid;
}

在任何情况下，最好的方法是检查给定字符串的长度。如果你的字符串是myString，那么代码是:

    int len = [myString length];
    if(len == 0){
       NSLog(@"String is empty");
    }
    else{
      NSLog(@"String is : %@", myString);
    }

最好的方法是使用分类。 您可以检查以下功能。它有所有需要检查的条件。

-(BOOL)isNullString:(NSString *)aStr{
        if([(NSNull *)aStr isKindOfClass:[NSNull class]]){
            return YES;
        }
        if ((NSNull *)aStr  == [NSNull null]) {
            return YES;
        }
        if ([aStr isKindOfClass:[NSNull class]]){
            return YES;
        }
        if(![[aStr stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length]){
            return YES;
        }
        return NO;
    }

//Different validations:
 NSString * inputStr = @"Hey ";

//Check length
[inputStr length]

//Coming from server, check if its NSNull
[inputStr isEqual:[NSNull null]] ? nil : inputStr

//For validation in allowed character set
-(BOOL)validateString:(NSString*)inputStr
{
    BOOL isValid = NO;
    if(!([inputStr length]>0))
    {
        return isValid;

    }

    NSMutableCharacterSet *allowedSet = [NSMutableCharacterSet characterSetWithCharactersInString:@".-"];
    [allowedSet formUnionWithCharacterSet:[NSCharacterSet decimalDigitCharacterSet]];
    if ([inputStr rangeOfCharacterFromSet:[allowedSet invertedSet]].location == NSNotFound)
    {
        // contains only decimal set and '-' and '.'

    }
    else
    {
        // invalid
        isValid = NO;

    }
    return isValid;
}

你可以检查你的字符串是空的或不是我使用这个方法:

+(BOOL) isEmptyString : (NSString *)string
{
    if([string length] == 0 || [string isKindOfClass:[NSNull class]] || 
       [string isEqualToString:@""]||[string  isEqualToString:NULL]  ||
       string == nil)
     {
        return YES;         //IF String Is An Empty String
     }
    return NO;
}

最佳实践是创建一个共享类UtilityClass并使用这个方法，这样你就可以通过在应用程序中调用它来使用这个方法。

你有两个方法来检查字符串是否为空:

让我们假设你的字符串名字是NSString *strIsEmpty。

方法1:

if(strIsEmpty.length==0)
{
    //String is empty
}

else
{
    //String is not empty
}

方法2:

if([strIsEmpty isEqualToString:@""])
{
    //String is empty
}

else
{
    //String is not empty
}

选择上述任何一种方法，了解字符串是否为空。